PTCB Certified Pharmacy Technician (PTCE)MedicationsHard
A pharmacy technician receives a prescription for 'warfarin 5 mg, take 1 tablet daily.' The patient's chart shows a new prescription for 'trimethoprim/sulfamethoxazole DS.' What potential drug interaction should the technician be aware of and bring to the attention of the pharmacist?
- AIncreased risk of nephrotoxicity
- BIncreased risk of hyperkalemia
- CIncreased risk of bleeding
- DDecreased effectiveness of warfarin
Show answer & explanationAnswer & explanation
Correct answer: C. Increased risk of bleeding
Trimethoprim/sulfamethoxazole (Bactrim) is a known inhibitor of CYP2C9, the primary enzyme responsible for metabolizing warfarin. This inhibition can lead to increased warfarin levels, enhancing its anticoagulant effect and significantly raising the risk of bleeding. This is a critical drug-drug interaction.
Why the other options are wrong
- A. Nephrotoxicity can occur with trimethoprim/sulfamethoxazole, especially in dehydrated patients, but it's not the primary interaction with warfarin.
- B. Hyperkalemia is a known side effect of trimethoprim, but not the primary interaction with warfarin.
- D. Incorrect. The effectiveness of warfarin would be increased, not decreased.
Drug-Drug Interaction (Pharmacodynamic)
When the effects of one drug are altered by the presence of another drug in the body, often due to competition for receptors or changes in physiological response.
- Can result in additive, synergistic, or antagonistic effects.
- May lead to increased toxicity or decreased efficacy.
- Requires careful monitoring and potential dosage adjustments.
Memory trick: Warfarin's a Wimp, Watch What You Mix, or Bleeding's the Blight!